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DIY shutter speed meter made of logic chips

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Caliaxy:
I'm wondering how fast you can strobe the LEDs before they seem continuously lit and how this compares with the persistence of the phosphor on the CRT of an analog oscilloscope. You might win  ;)

graybeard:

--- Quote from: Caliaxy on February 07, 2020, 05:00:40 pm ---I'm wondering how fast you can strobe the LEDs before they seem continuously lit and how this compares with the persistence of the phosphor on the CRT of an analog oscilloscope. You might win  ;)

--- End quote ---

The persistence of a LED is limited by the storage time of the minority carriers, typically in ns to the low tens of ns.  GaN LEDs other than blue or UV use phosphors with a longer decay time, typically in the low 100s of ns that limits how fast they can turn off.

The decay time of CRT phosphors varies from a few ms to tens of seconds.

The turn off time of LEDs can be limited by the driving circuit turn of time as well.

graybeard:

--- Quote from: plazma on February 05, 2020, 05:50:04 pm ---I needed to verify the shutter speed of a CMOS camera. I ended up making a quick'n'dirty circuit of D-type flip flops.
There are 30 SMD leds in a row. One illuminated led is stepped every clock pulse. The led low side is controlled with an N-fet which is also connected to the clock signal. One led is on when the clock is high. This way the led duty cycle & brightness can be controlled by adjusting the clock duty cycle.

--- End quote ---

If the clock is 1kHz the led is stepped every 1ms. With a 10ms integration time there are 10 leds illuminated in the picture.


--- End quote ---

That is a clever solution.

Peabody:
Can you demonstrate rolling shutter with this setup by setting the LEDs vertical, or even diagonal?  Or would all the lines be straight because the subject isn't actually moving with respect to the camera?

plazma:
I can try it and see if there is any interesting effect caused by the rolling shutter.

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